GALVANISED BOX AND MATTRESS GABIONS

PVC Coated Galvanised Gabions

PVC Coated Galvanized Gabions: Box 2 X 1 X1 mesh made of hexagonal triple twisted wire mesh complying with BS1485, galvanized to meet BS 443, wire diameter 3.00mm. Mattress 3X2X0.30.

We supply technical details of the gabion work fabricated from box and mattress for European customers.

Plastic Coated Galvanised Steel Woven Mesh Gabions

Gabion Works for River Bedding Protection

Gabion Works with Box and Mattress
Gabion works are formed with box and Mattress gabions placed fill material as specified.
The gabions shall be flexible zinc coated gabions fabricated of wire mesh. Each gabion
shall be divided by diaphragms into cells whose length shall not be greater than the width of the gabion plus 100 millimetres, so that down slope distance between vertical partitions never exceeds 1100 mm.

Mattresses Forming
The foundation for each gabion and mattress shall be prepared to the satisfaction of the Engineer. Irregularities in the foundation shall be excavated or tightly filled with gravel to produce a surface, which has no protrusions or cavities in excess of 100 mm.

Prior to placing mattresses the foundation shall be covered by a permeable geotextile membrane in accordance with the requirements.

The mattresses shall be flexible galvanised gabions of the size per required and shall be fabricated from wire mesh and selvedge. Each mattress shall be divided by diaphragms into cells, whose length shall not be greater than the width of the gabions or mattresses plus 100 mm. The gabion and mattress boxes shall be fabricated and supplied by an approved manufacturer. The prefabricated mattresses shall be obtained complete with sufficient suitable galvanised wire for completing the wiring of the gabions and mattresses on Site. The wire in the gabions and mattresses shall be galvanised similar to or stronger than that used in galvanised gabions. The wires in the gabions and mattresses shall be arranged so that the spacing between the wires is as per the international accepted standards.

The gabions and mattresses shall be assembled and filled in accordance with the manufacturer's instructions or as otherwise approved.

Geotextile Fabrics:
Permeable geotextile membranes shall be installed beneath mattresses and elsewhere as directed. The permeable membrane shall have the following properties:
Nominal weight (g/m2) 350
Water flow (l/m2/s) at 100 mm head 35

The membrane shall be laid in accordance with the manufacturer's instructions except that the minimum overlap at the edges and ends of the fabric shall be 1.0 m. During storage, the rolls of fabric to be used for the membrane shall be sheltered from water and direct sunlight. Backfill material shall be placed in such a way that no damage, or movement of the membrane sufficient to leave the foundation unprotected, takes place. The membrane shall be covered within 24 hours of unrolling to limit exposure to sunlight. No vehicular traffic will be permitted on the membrane after installation.

Wire Fabric for Gabions:
The fabric shall be triple-twisted hexagonal woven steel wire mesh complying with BS 1485. The wire shall be galvanized before weaving and test samples shall meet the requirements of BS 443.
Wire diameter and mesh size shall be 3.0 mm and 80 x 100 mm respectively.
The wire mesh shall have sufficient elasticity, equivalent to a minimum of 10% of the length of a section of mesh under test without reducing the diameter or tensile strength of the individual wires.
The selvedging must be such that the mesh will not unravel and the strength of the connection between the selvedge wire and the mesh shall be equal to or greater than the breaking strength of the mesh.

PVC coating is required for the mesh wire, standard tie wires, standard binders, internal connecting wires, preformed stiffeners, and selvage wire.
PVC coating must be UV resistant. A suitable UV resistance additive must be blended with the PVC and the colour of the PVC coating must be gray and resistant to fading.
Apply the zinc coating before applying the PVC coating. Application of the PVC coating must comply with the manufacturer's instructions.
The PVC coating must be evaluated by infrared spectral scan and the results submitted for approval before any orders are placed.
The minimum thickness of the PVC coating must be 0.35mm when measured radially at any cross-section transverse to the wire length.
PVC coating will be visually inspected. There must be no nicks, cuts, holidays, or abraded
areas. Minor cuts, nicks, and other minor imperfections due to manufacturing are allowed along the selvage-wrapped edges of the twisted wire mesh.

Binding and Connecting Wire

Sufficient binding and connecting wire must be supplied with the gabions to perform all the wiring operations to be carried out in the construction of the gabion work. The diameter of the selvedge wire shall be 3.90 mm or greater for both box gabions and mattresses. The diameter of lacing wire shall be 2 40 mm. These wires shall be galvanised and PVC coated as well.

Tolerances for Gabions and Gabion Wire
Gabion and gabion materials shall be manufactured to the following tolerances:
Gabion Dimensions
A tolerance of + 10% on the width and height of the gabion and a tolerance of - 10% on the
length shall be permitted.
Mesh Dimensions
• A tolerance of - 15% on the nominal size of the mesh shall be permitted.
Wire Thicknesses
• A tolerance on the diameter of all wire in the above Clauses of - 2.5% shall be permitted
in accordance with BS 1052. The weight of gabions is therefore subject to a tolerance
of - 5%.
• Gabions incorporated in the permanent works shall be such that on average their
dimensions shall conform to requirements.

Method of Construction of Gabions
Gabions shall be assembled using manufacturer's assembly instructions.
Prepare the formation for pitching and gabions by trimming the excavation accurately to the specified dimensions. Where over-excavation occurs it shall be backfilled with compacted fill or, if a gravel backing is used, with the gravel backing material, all to the approval of the Engineer and at the expense of the Contractor. Gabion mattresses placed on the spillway section of embankments shall be aligned with their long dimension downslope such that the maximum compartment dimension measured downslope is 1.0m. Where two layers exist, the upper layer shall be laid directly upon the lower layer and all adjacent selvedge wires shall be laced.

The gabions shall be unpacked, unfolded on a hard flat surface, stretched out and stamped out of any unnecessary creases. The sides and internal diaphragms shall be raised to the vertical and checked to see that heights are the same and correct. The diaphragms shall be pulled upright to the same height as sides and wired to the sides using the same helical wire connecting each diaphragm to the bottom of the gabion.

Every contact between boxes or between diaphragms and boxes or between lids and boxes shall be laced.
Individual lacing wire shall be minimum 2 000mm long and lacing wires shall be joined. All lacing shall be done as a continuous lacing operation and the wire shall pass through every mesh with double turns. Lacing wire shall be laced around selvedges or wire mesh. All connections between lacing wires shall be 5 (five) close turns by pliers.

The wired-up gabions shall be carried to the final position, if not assembled at the final position, and wired securely to the adjoining gabions to give a continuous joint along the adjacent edges, including the bottom edges. They shall be placed and wired together empty.

Where appropriate, units should be placed on headers and stretchers in alternate courses, and vertical joints should not be continuous but staggered. However, the lacing between top and bottom layers must continue as for adjacent boxes.

Before filling, the gabions shall be accurately positioned in their required location, straightened to remove all kinks in the wire mesh and tensioned to avoid bulges occurring during filling. The method adopted for tensioning the gabions shall be to the approval of the Engineer. Completed gabions shall be inspected and approved by the Engineer before filling commences.

Gabions may be filled by hand. The stones must be tightly packed to minimize the formation of voids. The size of a void shall not be greater than the minimum particle size specified and the voids ratio shall be less than 30%. The filling shall start at the bottom if the gabions are laid on a slope. Particular care must be taken to avoid the use of flat stones as these do not compact properly and cause the gabions to bulge.

In box gabions with exposed faces, bracing wires shall be fixed laterally and vertically in accordance with manufacturer's assembly instructions or as ordered by the Engineer. Care should be taken to ensure that the bracing wires are evenly tensioned to avoid bulges occurring in the gabion face.

Gabions shall be overfilled by 50 mm to allow for settlement. Gabion lids shall be stretched tightly over the fill material and securely wired down to the edges as well at to the diaphragms. If voids are formed between the fill and the gabion lid, then these may be filled with small stones provided that no small stones occur on an exposed face.

The gabion mesh shall be cut, folded and wired together to form mitre joints, angles, curves or slopes which are not possible to obtain in the structures with the standard rectangular gabions. The mesh must be cleanly cut, and the surplus mesh cut completely out, or folded back or on to, and neatly wired to an adjacent gabion face. The cut edges of the mesh shall be securely laced together with binding wire. Wherever possible, gabions shall be cut, folded and wired in a region where relatively low flow velocity occurs. Sizes of gabions shall be as ordered by the Engineer.

Tolerances for Completed Gabion Structures
When completed, gabion boxes should be straight and vertical and free from bulges or kinks in the wire mesh. If bulges do occur in a box gabion, then the maximum allowable departure from vertical, as measured with a plumb bob from the top or bottom selvedge wire shall be 50 mm. Sags shall not be allowed.

Workmanship for Gabion Structures
Before the gabion works are allowed to proceed fully, the Contractor will construct and fully complete a minimum length of 10m to the satisfaction of the Engineer. During the construction of this sample length, the Contractor will ensure that his site staff becomes fully familiar with the construction techniques required to achieve an acceptable level of workmanship.
During the construction of the remaining works, the sample length will be used as a reference to ensure that the same level of workmanship is maintained throughout the Contract.

Stones for Gabions and Gabion Bedding
Stones for gabions shall be clean, natural, hard and durable with the minimum specific gravity, soundness and abrasion resistance as specified.

The borrow areas for gabion fill shall be approved by the Engineer and shall be located as
close to the Site as possible. The Contractor shall adopt a method of extraction, which will
produce material of consistent and uniform quality of the required grading. Material for gabion fill shall be obtained from the Wadi bed provided the above requirements are satisfied. Stone for gabions will be generally well graded boulders ranging between 60mm and 250mm.
Rocks for gabion baskets equal to or greater than 600mm in height must vary in size and
comply with the gradation:
Rock Grading for 600mm or Larger Baskets
Screen size (mm) Percentage passing
300 100
100 5 to 15
80 0 to 5
Rocks for gabion baskets or mattresses that are 300mm in height must vary in size and comply with the gradation shown in the following table.
Rock Grading for 300mm Baskets
Screen size (mm) Percentage passing
200 100
100 5 to 20
80 0 to 10

The unit weight of a rock-filled gabion must be at least 18 kN/m3. Whenever requested by the Engineer the unit weight of completed baskets or mattresses shall be verified. Certified scales shall be used for weighing and the unit weight shall be calculated using the theoretical volume of the basket.